konami.js

/**
 * Trigger callback when the user inputs the konami code
 * @param {Function} callback
 * @returns {Function} event handler
 */
function konami(callback) {
    'use strict'
    let kkeys = []
    // up,up,down,down,left,right,left,right,B,A
    const konami = '38,38,40,40,37,39,37,39,66,65'
    return event => {
        kkeys.push(event.keyCode)
        if (kkeys.toString().indexOf(konami) >= 0) {
            callback(event)
            kkeys = []
        }
    }
}

const handler = konami(console.log)

window.addEventListener('keydown', handler)